This invention relates to jet printers, including jet printers for direct-to-plate printing systems.
Ink-jet printers operate by charging drops of ink with a charging electrode and guiding them to a print substrate through a high intensity electric field. Printers can modulate the charge on an ink drop by changing the charging electrode voltage to select whether each drop is to be printed or instead sent to a gutter. Printers may also adjust the charging voltage to compensate for aerodynamic effects and for the influence of the charge from adjacent drops. Some printers employ a technique known as xe2x80x9cswathingxe2x80x9d to continuously change the field and thereby direct drops from one or more stationary ink jets to different locations on the printing substrate, instead of moving a print head across the substrate.
Jet printing techniques are applicable to direct-to-plate printers. Such printers typically apply a printing fluid to a sheet of plate stock mounted on a drum. This fluid causes changes in the portions of the surface of the plate on which it is deposited. Although further processing of the plate may be necessary, the result is a printing plate that can serve to print large numbers of pages.
In one general aspect, the invention features a jet printer that includes a jet printing fluid source, at least one deflection element located proximate an output trajectory of the fluid source, a digital filter, and a digital-to-analog converter operatively connected between an output of the filter and at least the deflection element.
The printer can further include a processor portion operative to drive the printer to print half-tone images on a print substrate, which can be a printing plate. The printer can further include a drum having a print substrate mounted on the drum, and a carriage mechanism for moving the jet printing fluid source and the deflection element perpendicular to a feed direction of a print substrate, which can be a printing plate. The printer can further include a swathing table, and a control circuit responsive to the swathing table and having an output operatively connected to the digital filter. The digital filter can be constructed and adapted to operate on a desired position for a printing fluid drop, on previous desired positions for printing fluid drops from the jet printing fluid source, and on previous outputs of the filter. The digital filter is an IIR filter. The digital filter can have a transfer function that includes a sum of previous input position values each multiplied by one of a first plurality of coefficients, and previous output deflection values each multiplied by one of a second plurality of coefficients.
In another general aspect, the invention features a jet printer that includes a drum having a print substrate mounted on it, a movable carriage, and a jet printing fluid source attached to the carriage. At least one deflection element is located proximate an output trajectory of the jet printing fluid source, and a carriage mechanism is provided for moving the carriage along a direction of an axis of rotation of the drum. The printer also includes a swathing table, and a control circuit responsive to the swathing table and having an output provided to at least the one deflection element.
The deflection element can be a charging tunnel surrounding an output of the jet printing fluid source or one of a pair of deflection electrodes. The jet printer can further include a processor portion operative to drive the printer to print half-tone images on a print substrate. A print substrate placed in the output trajectory of the jet printing fluid source can be a printing plate. A drum actuation controller can be provided which is synchronized with the control circuit to cause printing by the printer to take place according to a helical progression.
In a further general aspect, the invention features a method of jet printing, that includes electromagnetically guiding charged drops of printing fluid to a print substrate through a electromagnetic field, applying a digital filtering function to a desired input position value, to obtain a guiding value for a further drop of printing fluid, and electromagnetically guiding the further charged drop of printing fluid to the substrate.
The step of applying can apply a transfer function that includes a sum of previous input position values each multiplied by one of a first plurality of coefficients, and previous guiding values each multiplied by one of a second plurality of coefficients.
In another general aspect, the invention features a method of jet printing that includes moving a jet printing fluid source to a first position along a direction of an axis of rotation of a print substrate, electromagnetically guiding a first drop of printing fluid from the jet printing fluid source at the first position so that it lands on the print substrate at a first distance along the direction of the axis of rotation of the print substrate, rotating the print substrate relative to the jet printing fluid source about the axis of rotation after the step of electromagnetically guiding a first drop, and electromagnetically guiding a second drop of printing fluid from the jet printing fluid source at the first position so that it lands on the print substrate at a second distance along the direction of the axis of rotation of the print substrate after the print substrate has rotated, wherein the second distance is different from the first distance.
The method can further include electromagnetically guiding further drops of printing fluid from the jet printing fluid source at the first position so that the further drops land on the print substrate at further different distances along the direction of the axis of rotation of the print substrate, after the print substrate has rotated further. The steps of guiding and rotating can form a part of a half-tone printing process.
In a further general aspect, the invention features a jet printer that includes means for electromagnetically guiding each of a plurality of charged drops of printing fluid to a print substrate through an electromagnetic field, means for applying a digital filtering function to a desired input position value and to values of charge on the drops relative to the electromagnetic field, to obtain a deflection value for a further drop of printing fluid, and means for converting the deflection value to an electromagnetic field intensity to guide the further drop to the substrate.
The means for of applying a digital filtering function can apply a transfer function that includes a sum of previous input position values each multiplied by one of a first plurality of coefficients, and previous deflection values each multiplied by one of a second plurality of coefficients.
In another general aspect, the invention features a jet printer that includes means for moving a jet printing fluid source to a first position along a direction of an axis of rotation of a print substrate, means for rotating the print substrate relative to the jet printing fluid source about the axis of rotation, and means for electromagnetically guiding a first drop of printing fluid from the jet printing fluid source at a first position so that it lands on the print substrate at a first distance along the direction of the axis of rotation of the print substrate, for electromagnetically guiding a second drop of printing fluid from the jet printing fluid source at the first position so that it lands on the print substrate at a second distance along the direction of the axis of rotation of the print substrate after the print substrate has rotated, wherein the second distance is different from the first distance.
The means for electromagnetically guiding can further be for guiding the first and second drops at locations that are spaced apart both longitudinally and radially with respect to the axis of rotation. The printer can further include means for causing the means for guiding to perform a half-tone printing process.
Systems according to the invention can be advantageous in that they provide an inexpensive, accurate and flexible method of controlling the trajectory of drops of printing fluid in jet printing. By treating drops as samples in a sampled-data system, printers can perform swathing, aerodynamic compensation, and adjacent drop compensation in the digital domain using an existing printer control processor or an inexpensive add-on microprocessor. Such printers can also be reconfigured for different printing applications without requiring a redesigned analog circuit, and they may even be digitally calibrated at start-up or on-the-fly to improve print characteristics. These features can improve the quality of printing, and can reduce the cost and time involved in developing improved printers.
Systems according to the invention may also permit printing operations to take place more quickly and efficiently, in moving-head, direct-to-plate, jet printers. Swathing can permit such printers to deposit individual charged drops that are spaced apart in two polar dimensions on a plate as it rotates. This allows for fine-pitch printing at high speeds with a minimum number of guard drops.